PROJECT ABSTRACT Excessive digital media use has been linked with several adverse health outcomes in children, including obesity, disrupted sleep, externalizing behavior, and executive functioning deficits, but measurement tools have not kept pace with the advancements in digital technology now used in most American households. For example, most American families with young children now own a smartphone (95%) or tablet (78%), and mobile device-based activities comprise a growing proportion of the time children spend with screen media on a given day. Most studies examining child and parent media use rely on parent-report questionnaires or time use diaries, but preliminary evidence suggests that these methodologies may be inaccurate or biased when measuring mobile device use. This poses a measurement challenge for researchers, which in turn has created an evidence gap and calls for higher quality research on children and media. To address this gap in knowledge, this STTR phase I grant application aims to further develop an existing mobile sensing app, Chronicle, through an ongoing collaboration between OpenLattice (a data integration firm specializing in social research) and the CAFE Consortium (a multi-institution, cross-disciplinary group of early childhood media researchers, of which Dr. Radesky is a member). This application aims to develop Chronicle with the following Specific Aims: 1) Automation of data reduction and analysis, with creation of a study team dashboard from which investigators can visualize and export their participants? mobile device usage data without the need for complicated data processing steps; 2) Addition of ecological momentary assessment (EMA) features, which will allow investigators to study the cascades of emotions, cognitions, or behaviors that contribute to or stem from media use in families? daily lives; 3) Addition of user awareness features, so that data from shared mobile devices can be annotated and analyzed by user (e.g., parent, child, or co-viewed). We will test whether these features can be feasibly implemented by cross-disciplinary research groups in order to create a flexible, scalable measurement tool. Through unobtrusive data collection of mobile media use, coupled with intermittent sampling of the user and context, we have the potential to fill substantial measurement gaps in the growing field of digital media and child health. An updated Chronicle measurement tool will allow more widespread use of high-quality media and daily measures by child health and development researchers and social scientists. No other such data collection tools are available, yet are needed due to the changing nature of media exposure as well as recent calls for greater understanding of children?s daily media use, health, and development.